1. Field of the Invention
The present invention relates to an exhaust gas purification apparatus for an engine for reducing and purifying nitrogen oxides (NOx) contained in exhaust gas from an engine.
2. Description of Related Art
An exhaust gas purification apparatus disclosed in Japanese Laid-Open (Kokai) Patent Application Publication No. 2003-293740 is proposed as a catalyst purification system for purifying NOx contained in exhaust gas from an engine. This exhaust gas purification apparatus injection-supplies a liquid reducing agent or a precursor thereof at a flow rate in accordance with an engine operation state to exhaust gas on an exhaust upstream side of a NOx reduction catalytic converter disposed in an exhaust passage, so that NOx is subjected to selective reduction reaction with the reducing agent in the NOx reduction catalytic converter. Thus, NOx is purified and converted into harmless components.